Chapter 9 Study Guide: Solutions (GOB Chemistry)

Chapter 9: Solutions

Introduction to Solutions

Solutions are homogeneous mixtures composed of two or more substances. In chemistry, understanding solutions is essential for studying reactions, concentrations, and properties of mixtures. This chapter covers the definitions, classifications, and calculations related to solutions.

• Solution: A homogeneous mixture of two or more substances.

• Solute: The substance that is dissolved in a solution.

• Solvent: The substance that does the dissolving, usually present in greater amount.

• Solubility: The maximum amount of solute that can dissolve in a given amount of solvent at a specific temperature.

• Saturated Solution: Contains the maximum amount of dissolved solute at a given temperature.

• Unsaturated Solution: Contains less solute than the maximum amount that can dissolve.

• Supersaturated Solution: Contains more solute than is normally possible at a given temperature.

Types of Solutions and Classification

Solutions can be classified based on the physical state of the solute and solvent, as well as their ability to conduct electricity.

• Electrolyte: A substance that dissolves in water to give a solution that conducts electricity.

• Nonelectrolyte: A substance that dissolves in water to give a solution that does not conduct electricity.

• Homogeneous Mixture: Uniform composition throughout (e.g., salt water).

• Heterogeneous Mixture: Non-uniform composition (e.g., oil and water).

Concentration Units

Concentration expresses the amount of solute present in a given quantity of solvent or solution. Several units are used in chemistry to describe concentration.

• Molarity (M): Moles of solute per liter of solution.

• Mass/Volume Percent (% m/v): Grams of solute per 100 mL of solution.

• Volume/Volume Percent (% v/v): mL of solute per 100 mL of solution.

• Mass/Mass Percent (% m/m): Grams of solute per 100 g of solution.

Key Formulas:

• Molarity: $M = \frac{\text{mol solute}}{\text{L solution}}$

• Mass/Volume Percent: $\% (m/v) = \frac{\text{g solute}}{\text{mL solution}} \times 100$

• Volume/Volume Percent: $\% (v/v) = \frac{\text{mL solute}}{\text{mL solution}} \times 100$

• Mass/Mass Percent: $\% (m/m) = \frac{\text{g solute}}{\text{g solution}} \times 100$

Preparation and Dilution of Solutions

Solutions are often prepared by dissolving a known amount of solute in a solvent. Dilution involves adding more solvent to decrease the concentration of a solution.

• Dilution Equation: $C_1 V_1 = C_2 V_2$

• Application: Used to calculate the volume or concentration needed when diluting solutions.

• Example: If you have 0.45 M NaCl and want to prepare 75 mL of 0.15 M NaCl, use the dilution equation to find the volume of stock solution needed.

Solubility Rules and Table

Solubility rules help predict whether a compound will dissolve in water. These rules are often summarized in tables provided in textbooks or on the back of the periodic table.

Compound Type	Solubility in Water
Group 1 ions (Li+, Na+, K+)	Soluble
Nitrates (NO3-)	Soluble
Chlorides (Cl-)	Soluble (except Ag+, Pb2+)
Sulfates (SO42-)	Soluble (except Ba2+, Pb2+, Ca2+)
Carbonates (CO32-)	Insoluble (except Group 1 and NH4+)
Phosphates (PO43-)	Insoluble (except Group 1 and NH4+)
Hydroxides (OH-)	Insoluble (except Group 1, Ca2+, Ba2+)

Additional info: Table entries inferred from standard solubility rules.

Properties and Behavior of Solutions

Solutions exhibit unique properties such as boiling point elevation, freezing point depression, and osmotic pressure. These properties depend on the concentration and nature of the solute.

• Boiling Point Elevation: Addition of solute increases the boiling point of the solvent.

• Freezing Point Depression: Addition of solute lowers the freezing point of the solvent.

• Osmosis: Movement of solvent through a semipermeable membrane from low to high solute concentration.

Sample Problems and Solutions

Practice problems help reinforce understanding of solution concepts. Here are examples based on the study guide:

• Example 1: Will CH4 dissolve in water? Answer: No, CH4 is nonpolar and will not dissolve in polar water due to lack of intermolecular forces.

• Example 2: Calculate the volume of 0.45 M NaCl needed to make 75 mL of 0.15 M NaCl. Solution: $C_1 V_1 = C_2 V_2$ $0.45 \times V_1 = 0.15 \times 75$ $V_1 = \frac{0.15 \times 75}{0.45} = 25$ mL

• Example 3: What is the mass/volume percent of a solution made by dissolving 4.0 g NaOH in 100 mL water? Solution: $\% (m/v) = \frac{4.0}{100} \times 100 = 4.0\%$

Key Terms to Know

• Solution

• Solute

• Solvent

• Homogeneous mixture

• Heterogeneous mixture

• Solubility

• Saturated/Unsaturated/Supersaturated

• Electrolyte/Nonelectrolyte

• Molarity

• Concentration

• Mass/Volume Percent

• Osmosis

• Boiling Point Elevation

• Freezing Point Depression

Additional Resources

• Concentration Simulation

• Molarity Simulation

• Sugar & Salt Simulation

• Solution Vocabulary Practice

Additional info: Some explanations and table entries have been expanded for academic completeness and clarity.